Posted
by
CowboyNeal
on Thursday October 11, 2007 @09:12PM
from the objects-in-mirror-may-be-closer-than-they-appear dept.

twilight30 writes "Discovery News is reporting that 'One of the most famous and scrutinized heavenly objects is 10 to 20 percent closer than we thought, say two teams of radio astronomers who have made some of the most precise cosmic distance measurements ever, with a telescope nearly as big as Earth. The Orion Nebula is the closest major stellar nursery to Earth, so it has been heavily studied to learn about the lives of stars. Its distance from Earth, however, has long been a matter of uncertainty, with an estimate made about 25 years ago in need of revision.'"

The VLBA was aimed at one of the few radio-wave emitting stars in Orion, which was viewed twice in a single a year. The almost 200-million-mile width of Earth's orbit around the sun allowed the VLBA to serve as one eye, then again as the other eye six months later.

Wouldn't that be a telescope 200-million-miles wide, using the same poetic license that led them to say they used a telescope as big as the earth.

Saying that the telescope was "nearly as big as Earth" is dead wrong. The effective aperture of the telescope, for this purpose, is twice the radius of the orbit of Earth around the sun, or almost 200 million miles. Gotta love those science reporters...

Wrong again. The 2 points, ~200 million miles apart were used as points in a measure of parallax. The virtual aperture of the VLBA scope is ~5000 miles diameter, which isn't *quite* "nearly as big as earth". Still a pretty big aperture, even though it's not a complete circular area, the resolution provided is apparently sufficient to measure the stellar (nebular?) parallax wrt M42.

What I find more interesting in this article is the close relationship alluded to between the trapezium and the nebula...

"Impacted"
Plot: In the year 2050 the Earth almost crashes into the Orion Nebula, only to be rescued from destruction by two nerdy radio astronomers from Parkes Observatory in the middle of nowhere in Australia, who, whilst trying to find a cure for constipation from eating too much McDongles(TM) Impact McBurglettes, find that by injecting massive amounts of First Fleet Enema into the Nebula they can cut a path through the Nebula. The romantic part of the movie is where the local district nurse shows up an

Um, I was replying to a comment on having to "start" doing space VLBI and specifically linked the WP topic on space VLBI. I've done the NRAO "boot camp" and published work from VLA data; I'm aware of the history of radio interferometry.

It's an interferometer [wikipedia.org]. It's not one telescope the size of earth but many smaller telescopes each collecting samples along a line with a length of about the diameter of Earth. The samples can be processed to give a picture with the resolution of a telescope the diameter of Earth (but it still only captures a small amount of em waves).

Correct me if I'm wrong, but isn't this basically measuring stellar parallax [wikipedia.org], but instead of using visible light and optical telescopes against a background of stars, they are using radio waves and radio telescopes against a background of quasars?

Don't be silly. It says 20% closer since 25 years ago. So it will be here in 100 years, as in 25 years it's traveled one-fifth of the way, so it only has four more fifths to travel.
Dibs on the Trapezium.

Very good question. I can only reply by pointing to the scalar polarisation effect negating the red/blue doppler shift you mention. Couple that with Newtonian dynamics in question, and you have a very good correction mechanism along the theta axis. Not to mention that the wibble-wobble isn't nearly as unstable as once thought.

the sun travels around the galactic center at about 20km/s. even assuming than sun and orion nebula travel away from each other at this speed, for 6 months they'd have moved away at about 6 billion km. this is about 0.00068 light years. since the distance is estimated at 1250+ l.y. give or take 50-60, the error due to the relative movement of the two objects seems accounted for.

"Just remember that you're standing on a planet that's evolving
And revolving at nine hundred miles an hour,
That's orbiting at nineteen miles a second, so it's reckoned,
A sun that is the source of all our power...."

I'm writing my astrophysics thesis right now, so I have all kinds of literature references at my fingertips!
Anyone want to know how to calculate the cross section of a neutralino and a sulphur atom? Hey, where did everyone go?

typo in my ole physics book. that makes the max distance 0.068 l.y., still well within the margin of error even accounting for the large beta expansion and the wobbling due to galactic core protuberances.

What a load of crap. The study didn't use doppler shift to measure the distance, it used parallax. Beta expansion is a made-up term (in terms of astronomy), and the "counter planar" rotation is also imaginary. But the biggest clue was that Anonymous Coward was supplying the information.

Aren't they measuring the distance to stars within a three-dimensional object? I would guess that they could pick two stars that appear close together along our line of sight and come up with wildly different distances. Now perhaps if they measured the distance to one of the Trapezium stars (a very bright formation thought to lie at the "heart" of the nebula) they could come up with some meaningful measurement of distance.
Just thought of something else. Let's find a really large repository for data and cr

Aren't they measuring the distance to stars within a three-dimensional object? I would guess that they could pick two stars that appear close together along our line of sight and come up with wildly different distances. Now perhaps if they measured the distance to one of the Trapezium stars (a very bright formation thought to lie at the "heart" of the nebula) they could come up with some meaningful measurement of distance. Just thought of something else. Let's find a really large repository for data and create a three-dimensional map of the nebula. Don't try to shove this single star data down my throat!

It is true that the nebula is three dimensional, but it is nowhere near 1/10th the distance from earth to the orion nebula. The margin of error associated with the "front" of the nebula with the "back" or "center" of the nebula is a fraction of a fraction of a percent. (and I purposely used relative terms to demonstrate where error can lie)

Additionally, they did not use line of sight. They were using radio telescopes making them able to "see" the star at the center of the nebula without necessarily havin

But if you have two points of Earth in it's rotation and one point of star you should be able to triangulate the distance. So tracking one star should be enough to give you a guess. I assume they picked multiple stars to get an average for all bodies in question. I actually would have been interested to run the photos (or radio information as is the case) and the progression information from about every month for the six month rotation through a program to compare stars movement and form an average on mo

Bower and his colleagues came up with a distance of 1,270 light-years, give or take 76 light-years. That compares with the previous estimate of 1,565 light-years, give or take 266.

There's still overlap in the uncertainties of the measurements. So it wasn't incorrectly measured, just measured with a 17% error margin. The only ones who are incorrect are the people who quote the estimate without including the uncertainty.

Orion nebula distance : 1500 light years. 10% of this : 150 light years. IF you suppose that it is getting closer by that distance, then it means roughly 5+ light years for every years for 25 years. Nothing goes at a speed of 5+ light years per year. At best all physical stuff can only goes at near c (1 light year per year;)...) with photon going at exactly c in vacuum. And we would remark the relativistic effect, at those speed with such an enormous mass... (is that even

Isn't the galaxy *lens*-shaped...;)Humour Disclaimer - yes, no medium change, therefore a refractive index ratio of 1... unless you count stars as being "like atoms" in that they are *relatively* small "solid" object with large spaces in between them, suspended in a "space". Then therefore we *do* have a medium change and a ratio of refractive indices: light passes from an area of space populated by N stars / lightyear^3 to an area of space with M stars / lightyear^3 where N << M, and the N popula

You can't combine statistics like that.We have no idea of the accuracy of either measurement (specifically because we don't actually know how far away it is).

What we do know is that the new measurement is more precise. It's probably also safe to assume that the new one's at least slightly more accurate.

The troubling bit is that the median of the new measurement is considerably lower than the original, and lies outside of the error bars of the original estimate. This suggests that there's a good chance tha

That's not how you combine numbers with error bars.
First, you do weighted average based on how small the error bars are:
1/(1/266+1/76+1/23) * (1565/266 + 1270/76 + 1350/23) = 1346 LY
And then to find the error, you take the square root of the sum of the squares of all the errors in the final number that are introduced by the errors in the initial numbers:
sqrt(1/(1/266+1/76+1/23) * ( (266/266)^2 + (76/76)^2 + (23/23)^2 ) = +- 7 light years.